Automatic transmission of electronic control type

ABSTRACT

Herein disclosed is an automatic transmission of electronic control type, which has hydraulic control for improving the shift feel of the automatic transmission. This automatic transmission includes an oil pressure source; a line pressure regulating valve for regulating the output oil pressure of the oil pressure a source to a line pressure; line pressure controller for sending an oil pressure signal for changing the line pressure to the line pressure regulating valve in response to an electric signal; an r.p.m. sensor for detecting the start and end of a shift; and an electronic controller for changing the electric signal to the line pressure controller stepwise in an open loop in a manner to correspond to the divisions of the shift which include at least starting, ending and intermediate stages.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automatic transmission of electriccontrol type and, more particularly, to the hydraulic control of ahydraulic control system for improving the shift feel of the automatictransmission at the time of a shift.

2. Description of the Prior Art

In the automatic transmission of the prior art, the line pressure, i.e.,the oil pressure to be fed to shifting components of the transmissionsuch as clutches or brakes is set according to the throttle opening, thegear ratio and the vehicle speed.

Since, however, the oil pressure during a shift is at a constant level,it is difficult to improve the shift feel.

FIG. 10 is a diagram showing the shifting characteristics of an examplein which the oil pressure is set to control the shift feel as well aspossible while retaining the durability of the engage components of theprior art.

As indicated at (a) in FIG. 10, the electronic control means decides anupshift from the 1st to 2nd speeds according to the input conditionsincluding the throttle opening and the vehicle speed and switches asignal to the shift solenoid from the 1st to 2nd speeds so as to effectthe upshift. Simultaneously with this, as indicated at (b) in FIG. 10,the line pressure of the transmission (T/M) is switched from that forthe 1st speed to that for the 2nd speed. Moreover, the engage pressureis also raised, as indicated at (c) in FIG. 10, to start the shift, andthe T/M input r.p.m. (=the engine r.p.m.) drops from the shift startingpoint and rises at the shift end, as indicated at (d) in FIG. 10. On theother hand, the output shaft torque during the shift changes, asindicated at (e) in FIG. 10. What invites trouble here is the torquefluctuations a and b which occur at the shift starting point (i.e., theengage starting point of the engage components) and the shift endingpoint which detract from the feel of the shift.

In order to reduce the aforementioned torque fluctuations, therefore, itis generally known to drop the oil pressure to be applied to the engagecomponents, as will be exemplified in the following.

FIG. 11 is a diagram of the shifting characteristics showing an examplein which the set oil pressure is dropped to improve the shift feel.

As indicated at (b) in FIG. 11, similar to FIG. 10, the line pressure isdropped from the aforementioned line pressure for the 2nd speed (thatis, the engage pressure slowly changes, as indicated at (c) in FIG. 11,and the T/M input r.p.m. changes, as indicated at (d) in FIG. 11). Then,the fluctuations of the output shaft torque at the shift starting/endingpoints are reduced to improve the shift feel. As indicated at (e) inFIG. 11, however, shift time t_(m2) is seriously lengthened. This meansthat the slip time of the engage components such as the clutches orbrakes is prolonged to the detriment of the durability of the engagementcomponents.

SUMMARY OF THE INVENTION

The present invention has an object to provide an automatic transmissionof electronic control type, which eliminates the above-specifiedproblems and improve the shift feel without deterioration of thedurability of the clutches or brakes.

In order to achieve the above-specified object, according to the presentinvention, there is provided an automatic transmission of electroniccontrol type, which comprises: an oil pressure source; a line pressureregulating valve for regulating the output oil pressure of said oilpressure source to a line pressure; line pressure control means forsending an oil pressure signal for changing the line pressure to saidline pressure regulating valve in response to an electric signal; anr.p.m. sensor for detecting the start and end of a shift; and means forchanging the electric signal to said line pressure control meansstepwise, in an open loop, in a manner to correspond to said divisionsof the shift, which include at least starting, ending and intermediatestages.

With the structure thus far described, according to the presentinvention, a fine hydraulic control can be accomplished by controllingthe hydraulic control solenoid in accordance with the shiftingsituations of the automatic transmission, after the shift signal hasbeen outputted, to change the oil pressure in multiple stages.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the following description to be made with referenceto the accompanying drawings, in which:

FIG. 1 is a diagram showing the overall system structure of an automatictransmission of electronic control type according to an embodiment ofthe present invention;

FIG. 2(a) and 2(b) are a diagram showing the hydraulic circuit of theautomatic transmission of electronic control type;

FIG. 3 is a schematic diagram showing the automatic transmission ofelectronic control type;

FIG. 4 is a table showing the operations of the automatic transmission;

FIG. 5 is a diagram showing the shifting characteristics of theautomatic transmission of electronic control type;

FIGS. 6(a) and 6(b) are a flow charts showing the line pressure controlof the present invention;

FIG. 7 is a time chart showing the line pressure control;

FIG. 8 is a table of the stored data of the gear stages against thethrottle opening of the present invention;

FIG. 9 is a flow chart for deciding the shift timings of the presentinvention; and

FIGS. 10 and 11 are diagrams showing the shifting characteristics of theprior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail in connection with theembodiment thereof with reference to the accompanying drawings.

As shown in FIG. 1, reference numeral 1 designates a T/M input r.p.m.sensor; numeral 2 a T/M output r.p.m. sensor; numeral 3 a throttleposition sensor (as will be shortly referred to as the "throttlesensor"); numeral 4 electronic control means acting as control means;numeral 5 an r.p.m. sensor input signal converter connected with the T/Minput r.p.m. sensor 1; numeral 6 an r.p.m. sensor input signal converterconnected with the T/M output r.p.m. sensor 2; numeral 7 a throttlesensor input signal converter connected with the throttle sensor 3;numeral 8 a CPU housing a memory and a timer; numeral 9 a first shiftsolenoid driver; numeral 10 a second shift solenoid driver; and numeral11 a linear solenoid driver.

As shown in FIG. 2, moreover, a hydraulic circuit is composed of atorque converter 31, check valves 32 and 38, a cooler 33, a coolerbypass valve 34, a lockup control valve 35, a lockup solenoid (i.e., afourth solenoid) 19, a lockup modulator valve 37, a secondary valve 27,a primary valve 26, a pressure relief valve 25, an oil pump 42, asolenoid modulator valve 24, a linear solenoid valve 23, an accumulatorcontrol valve 45, B₂ accumulators 46 and 47, C₂ accumulators 48 and 49,C₃ accumulators 50 and 51, B₁ accumulators 53 and 54, a 2-3 shift valve55, a second solenoid valve 18 having a second shift solenoid 13, a lowmodulator valve 59, a B₁ sequence valve 60, a neutral control valve 61,a manual valve 64, a 1-2 shift valve 65, a first solenoid valve 17having a first shift solenoid 12, and a 3-4 shift valve 67.

Thus, the automatic transmission of the present invention has the shiftmechanism shown in FIG. 3 and operates, as shown in FIG. 4.

Here will be described the hydraulic circuit to which a line pressurecontrol linear solenoid 22 relates, as shown in FIG. 1. The hydrauliccircuit is composed of: a clutch and brake hydraulic servo mechanism(although not shown) for engaging or releasing the predeterminedcomponents of the shift gear mechanism; and the primary valve 26 forregulating the line pressure to be fed to the hydraulic servo mechanismthereby to provide communication with control pressure coming from thelinear solenoid valve 23. In response to the signal coming from a linearsolenoid driver 11, the linear solenoid 22 of the linear solenoid valve23 operates the primary valve 26 in response to the line pressure datato control the oil pressure to be fed to the predetermined components.

FIG. 7 is a time chart showing an example of such line pressure control,and FIG. 8 is a table of the stored data of the gear stages against thethrottle opening, which are to be stored in a memory.

In FIG. 8, data (A) and (B) are composed of and stored in 1 byte bydividing 0 to 150% into 16 steps. As shown in FIG. 7, moreover, the oilpressure can be finely set according to the shift situations, after theshift signal has been outputted, by multiplying a reference oil pressureP_(L) by increments of 0 to 150%.

The oil pressure control in the automatic transmission of electroniccontrol type of the present invention will be described in the followingby exemplifying an upshift from the 1st to 2nd speeds as the shiftingcharacteristics.

As indicated at (a) in FIG. 5, the electronic control means 4 (as shownin FIG. 1) decides the upshift from the 1st to 2nd speeds on the basisof the data of the throttle opening and the vehicle speed and switchesthe signal to the shift solenoids from the 1st speed to the 2nd speed soas to effect the upshift. Simultaneously with this, the line pressure isswitched from the 1st to 2nd speeds, as indicated at (b) in FIG. 5.After T_(o) seconds from this switching, the line pressure is dropped to1 (i.e., the shift starting line pressure) so as to reduce the shock atthe time of starting the shift. This line pressure 1 is held till theshift start is decided in terms of the T/M input r.p.m., as indicated at(c) in FIG. 5.

Here, the time T_(o) is used to prevent the time period from beingelongated from the output of the shift signal to the start of the shiftand is set at T_(o) =0 seconds, unless otherwise especially necessary.

Next, in order to shorten the shift time from the shift start decisionto the shift end decision and to retain the durability of the engagecomponents, the line pressure is changed to and held at a higher level 2(i.e., the shifting line pressure higher than the level for the 2ndspeed but lower than the level for the 1st speed). In order to reducethe shocks at the end of the shift, moreover, the line pressure ischanged to and held at a lower level 3 for a time period T₁ (e.g., 1second) from the shift end decision. After the T₁ seconds from the shiftend decision, moreover, the line pressure is changed to the level forthe 2nd speed. At this time, the T/M input r.p.m. and the oil pressureto be fed to the engage components are so changed, as indicated at (d)and (e) in FIG. 5. Specifically, the fluctuations of the output torque,which are generated at the shift starting point and the shift endingpoint, are rounded, as indicated at a' and b', so that the shift shockscan be reduced.

Thus, after the switching of the shift signal, three kinds of oilpressures are newly set as those for the shift so that the oil pressurecontrol solenoids are controlled. As a result, the oil pressure controlcan be finely accomplished to improve the shift feel without diminishingthe durability of the engage components.

Here, the shift start decision and the shift end decision of the presentinvention are executed on the basis of the gear ratios before and afterthe shift and the r.p.m. coming from the T/M output r.p.m. sensor whenthe r.p.m. obtained from the T/M input r.p.m. sensor reaches thefollowing calculated values:

    Shift Start Decision: Nis≦K.sub.1 ×i.sub.1 ×N.sub.o ;

    and

    Shift End Decision: Nie≦K.sub.2 ×i.sub.2 ×N.sub.o,

wherein:

Ni: T/M Input R.P.M.;

K₁ : Constant (e.g., 0.8);

i₁ : Gear Ratio before Shift;

N_(o) : T/M Output R.P.M.;

K₂ : Constant (e.g., 1.1); and

i₂ : Gear Ratio before Shift.

The embodiment of the present invention will be described in thefollowing in connection with the line pressure control flow withreference to FIG. 6.

First of all, it is decided at Step 1 whether or not the shift signalhas been outputted. If YES, the shift flag is set at Step 2, and theT_(o) timer is started at Step 3. If NO, namely, if the shift signal isnot outputted, it is decided at Step 4 whether or not the automatictransmission is being shifted. If YES, it is decided at Step 5 whetheror not the time T_(o) has been elaspsed. If YES, the line pressureselect flag is set at Step 6 for the shifting. If NO, namely, the timeT_(o) is not elapsed, it is decided at Step 7 whether or not the shiftis started. If YES, the line pressure select flag is set at Step 8 forthe shifting. If NOT, namely, if the shift is not started, it is decidedat Step 9 whether or not the shift has been ended. If YES, the linepressure select flag is set at Step ○10 for the shift ending, and the T₁timer is started at Step ○11 . If NOT, namely, the shift is not ended,it is decided at Step ○12 whether or not the time T₁ has been elapsed.If YES, the line pressure select flag is set at Step ○13 for the steadystate, and the shift flag is cleared at Step ○14 . If NOT, namely, thetime T.sub. 1 is not reached, it is decided at Step ○15 whether or notthe transmission is being shifted. If YES, it is decided at Step ○16whether or not the shift is the upshift. If YES, either of two kinds ofdata (A) and (B) is selected at Step ○17 on the basis of the shiftdestination and the throttle opening. Next, the line pressure P_(L) isset at Step ○18 on the basis of the gear stage at present and thethrottle opening. Moreover, it is decided: at step ○19 whether or notthe line pressure is for shift-starting, at Step ○20 whether or not theline pressure is for ending the shift; and at step ○21 whether or notthe line pressure is for the shifting. In accordance with these decisionresults, respectively, the line pressures are controlled at Steps ○22 ,○23 and ○24 to the individual set levels.

Subsequently, the shift timing decide flow according to the embodimentof the present invention will be described with reference to FIG. 9.

First of all, it is decided at Step ○25 whether or not the shift signalhas been outputted already. If YES, the input r.p.m. Ni' is calculatedat Step ○26 on the basis of the T/M output r.p.m. from the T/M outputr.p.m. sensor and the gear ratio before the shift. Next, it is decidedat Step ○27 whether or not (Ni'-Ni)/Ni'≧0.1. If the result is YES, theshift start decision flag is set at Step ○ . Next, it is decided at Step○28 whether or not the shift has been started already. If the result isYES, the T/M input r.p.m. Ni" is calculated at Step ○29 on the basis ofthe T/M output r.p.m. and the gate ratio after the shift. Next, it isdecided at Step ○30 whether or not (Ni"-Ni)/Ni"≦0.1. If the result isYES, the shift end decision flag is set at Step ○31 .

Incidentally, in the foregoing embodiment, the line pressure controlmeans is exemplified by the linear solenoid which includes: anelectromagnet member for generating a pushing force in proportion to thecurrent value supplied; and a valve member having a spool driven by theelectromagnet member. Despite this fact, however, the linear solenoidmay be replaced by another actuator. This actuator may be a solenoidvalve such as a duty solenoid which is enabled to output a signal at anarbitrary oil pressure level by repeating its ON/OFF for a predeterminedfrequency.

Incidentally, the present invention should not be limited to theembodiment thus far described but can be modified in various manners onthe basis of the concept thereof without departing from the gist andscope of the following claims.

What is claimed is:
 1. An automatic transmission of electronic controltype, comprising:an oil pressure source; a line pressure regulatingvalve for regulating the output oil pressure of said oil pressure sourceto a line pressure; line pressure control means for sending an oilpressure signal, for changing the line pressure, to said line pressureregulating valve in response to an electric signal; an r.p.m. sensor fordetecting the start and end of a shift; and means for changing theelectric signal to said line pressure control means stepwise in an openloop in a manner to correspond to the divisions of the shift, whichdivisions include at least starting, ending and intermediate stages;wherein said r.p.m. sensor comprises a transmission output r.p.m. sensorand a transmission input r.p.m. sensor so that the shift start and endmay be decided on the basis of the gear ratios before and after theshift and the r.p.m. of the transmission output r.p.m. sensor,respectively, if the r.p.m. of the transmission input r.p.m. sensorreaches the following calculated values:

    Shift Start Decision: Nis≦k1×i1×No

    and

    Shift End Decision: Nie≦k2×i2×No

wherein:Ni: Transmission Input R.P.M.; k1: Constant (e.g. 0.8); i1: GearRatio before Shift; No: Transmission Output R.P.M.; k2: Constant (e.g.1.1); i2: Gear Ratio after Shift.
 2. An automatic transmission accordingto claim 1, wherein said line pressure control means comprises: a linearsolenoid including: an electromagnet member for generating a pushingforce in proportion to the current value supplied; and a value memberhaving a spool driven by said electromagnet member.
 3. An automatictransmission according to claim 2 wherein said transmission includes aninput shaft and wherein said transmission input r.p.m. sensor detectsrotation of said input shaft.
 4. An automatic transmission according toclaim 1 wherein said transmission includes an input shaft and whereinsaid transmission input r.p.m. sensor detects rotation of said inputshaft.